1. Field of the Invention
The present invention relates to a zoom lens, and more particularly, to a high-power zoom lens.
2. Background Art
Recently, high-power zoom lenses having a magnification exceeding 10 have been paid attention as an interchangeable lens for a single-lens reflex camera. Such a zoom lens is required to have high-quality imaging performance, and also required to be compact and low price. Depending on the favor for a digital single-lens reflex camera in recent years, a demand on these performances is increasingly growing in the zoom lenses for amateur use.
Since the high-power zoom lenses consist of a plurality of lens groups and should have moving mechanisms for moving the lens groups, the high-power zoom lenses tend to be bigger than the fixed focal length lenses. So, diameter of a filter or a lens barrel shall decrease because requirement for the compact zoom lenses is especially high among the performances from the viewpoint of portability and easy handling. On the other hand, an optical system having high imaging performance through selecting an inexpensive glass material should be achieved to reduce cost while maintaining a high level imaging performance. In recent years, zoom lenses with a full-time manual function have been popular. The full-time manual function enables instant switching to a manual focus mode in response to the rotation of a focus ring or the like even when the camera is set to an auto focus mode. Thus, the optical design of the optical systems in the zoom lenses have been complicated more and more because optical systems in the zoom lenses are also required to meet the new functions described above.
Then, as a conventional technology relating to the zoom lens, technologies disclosed in Japanese Patent Laid-Open Nos. 2009-271471, 2008-304952 and 2010-44103 exist. A zoom lens disclosed in Japanese Patent Laid-Open No. 2009-271471 consists of a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power arranged in this order from an object side to an image side and a plurality of lens groups move along an optical axis direction to change magnification. The second lens group functions as a focusing lens group. The second lens group moves in focusing to adjust the focus. As the zoom lens includes the optical system as described above, Japanese Patent Laid-Open No. 2009-271471 proposes a zoom lens that satisfies the conditions described later when a negative lens locates at closest to the object in a plurality of lenses constituting the second lens group is referred to as a lens 2a, and the refractive index and the Abbe number of the material for the lens 2a are n2a and ν2a respectively.[−0.0125*ν2a+2.175]<n2a<[−0.011*ν2a+2.21]42.0<ν2a<59.0
A zoom lens disclosed in Japanese Patent Laid-Open No. 2008-304952 consists of a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power arranged in this order from an object side. The respective lens groups move along an optical axis direction to increase distance between the first lens group and the second lens group, to decrease distance between the second lens group and the third lens group and changes distance between the third lens group and the fourth lens group to change magnification from a wide-angle end to a telescope end. The third lens group consists of a front group having a positive refractive power and a rear group having a negative refractive power arranged in this order from the object side and only the rear group moves in the direction perpendicular to the optical axis for image correction against camera shake. A zoom lens having a vibration compensation function that satisfies the following expression wherein the focal length of the zoom lens in a wide-angle end is fw and the focal length of the first lens group is f1 is proposed.1.5<[f1/fw]<8.0
Next, Japanese Patent Laid-Open No. 2010-44103 discloses a zoom lens consists of a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power arranged in this order from an object side. The respective lens groups move along an optical axis direction to increase distance between the first lens group and the second lens group, to decrease distance between the second lens group and the third lens group, and to decrease distance between the third lens group and the fourth lens group to change magnification from an wide-angle end to a telescope end. The second lens group as a focusing lens moves to the object side in focusing. In the optical system described above, a zoom lens having a vibration compensation function that satisfies the following expression wherein the focal length of the first lens group is f1, the focal length of the second lens group is f2, the focal length of the third lens group is f3, and the focal length of the entire optical system is ft is proposed in Japanese Patent Laid-Open No. 2010-44103.0.35<[f1/ft]<0.450.04<[|f2|/ft]<0.0650.15<[f3/ft]<0.25